A device casing is configured to include a first casing member provided with a hole including a guide hole and a fitting hole that communicates with the guide hole, and a second casing member provided with a protrusion at a position corresponding to the hole, the second casing member being configured to be fixed with respect to the first casing member by fitting the protrusion to the fitting hole. The guide hole guides movement of the protrusion that entered within the guide hole in an oblique direction when fixing the second casing member with respect to the first casing member so that the second casing member can get close to the first casing member in a state where the second casing member is guided in the oblique direction. The protrusion that moved in the oblique direction along the guide hole, passed through the guide hole and reached inside the fitting hole fits to the fitting hole. The second casing member is fixed with respect to the first casing member by the fitting of the protrusion to the fitting hole.